The size and weight of portable electronic devices have decreased significantly. Such electronic devices can be carried or worn by a user to provide service. As an example, 3D image displaying systems are currently experiencing explosive growth. As a result, associated devices such as shutter glasses used with 3D video players have seen an increase in use as well. A 3D video player can display a left image and right image, alternately, in order while it sends sync signals to the shutter glasses. After receiving a sync signal, the shutter glasses cause the left and right lenses to switch between an open and shielding state, respectively according to the timing of the sync signal. This enables users wearing the shutter glasses to see a left image with the left eye, and to see a right image with the right eye, so that the user perceives the correct 3D image. Another portable electronic device that is widely used is a Bluetooth headset Such a device can wirelessly receive an audio signal to play sound for a user.